Wide angle compact projection lens assembly

ABSTRACT

A wide angle lens assembly is symmetrically disposed about a central space wherein a reflecting component is positioned. The lens assembly is folded into a small space by use of a rightangled total reflecting prism in the central space. The lens system has a speed of f/ 4 and a total field angle of 90*. The outer lens components are negative to obtain a wide angle of view.

if a P7 Uni Miles [54] WIDE ANGLE COMPACT PROJECTION LENS ASSEMBLY [72]Inventor: John R. Miles, Glenview, Ill.

[73] Assignee: Microdlsplay Systems, Incl, New

York, N.Y.

[22] Filed: April 19, 1971 [2]] Appl. No.: 135,071

[52] US. Cl. ..350/216, 350/202, 350/204,

350/220 [5 1] Int. Cl. ..G02b 9/58 [58] Field of Search ..350/202, 215,216, 220, 203

[56] References Cited UNITED STATES PATENTS 3.209.649 10/1965 Macher..350/220 3,704,998 Dec. 5,1972

wen OR [451 FOREIGN PATENTS OR APPLICATIONS l,545,695 l0/l968 France..350/203 382,193 9/1923 Germany ..350/202 Primary Examiner-John K.Corbin Attorney- Albert F. Kronman [57] ABSTRACT A wide angle lensassembly is symmetrically disposed about a central space wherein areflecting component is positioned. The lens assembly is folded into asmall space by use of a right-angled total reflecting prism in thecentral space. The lens system has a speed off/ 4 and a total fieldangle of 90. The outer lens components are negative to obtain a wideangle of view.

1 Claim, 2 Drawing Figures PATENTEDuEc 5:912

FIG.

FIG. 2

INVENTOR. JOHN R. MILES ATTORNEY BACKGROUND OF THE INVENTION Wide anglelenses have been used for cameras and projection systems where a largearea of either an object or image is to be focused. Some prior lenses ofthis type have been described in US. Pat. Nos. 3,209,649; 2,376,091;2,713,809; and 2,845,845. The present invention differs from the priorart by having a considerable central space wherein a total reflectingprism can be positioned. The lens system is essentially symmetrical,having two outer negative lenses and two positive lens combinations oneither side of the central space. The positive lens combinations arecemented triplets with lenses of variable indices of refraction anddispersions to substantially correct for all the aberrations and producea flat image field.

One of the features of the present invention is the use of four negativelens elements two of which are cemented to each of two spaced positiveelements to correct for astigmatism when the field is flattened, andalso to correct for chromatic aberration.

Another feature of the invention is the novel arrangement of lenscomponents which produce a narrow substantially parallel bundle of raysat the center of the lens assembly where the reflecting prism or othertransparent block can be positioned.

For a better understanding of the present invention, together with otherdetails and features thereof, reference is made to the followingdescription taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a somewhat diagrammaticsectional view of a lens system having a right-angled total reflectingprism in the central space according to the present invention.

FIG. 2 is a sectional view of the system similar to FIG. 1 but showing aglass block at the central space and the optical axis as a straightline.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the FIGURES,indicates an entrance lens having a convex-concave negativeconfiguration made of crown glass with a low index of refraction. Lenselement 11 is a convex-concave negative lens separated from lens 10 byan axial space 8,. Lens element 11 is made of crown glass with a highindex of refraction. Lens element 12 is a positive double convex lenscemented to element 11. It is made of crown glass with a medium highindex of refraction. Lens element 13 is a concave-convex negative lenselement cemented to lens 12, made of crown glass with a low index ofrefraction.

The block or reflecting prism 14 is made of flint glass with a highindex of refraction to help avoid vignetting. The prism 14 is spaced adistance S, from lens 13. Lens element 15 is similar to lens 13 and ismade of crown glass with a low index of refraction. It is separated fromthe prism 14 by a distance 8,. Lens element 161s a positive doubleconvex element of crown glass with a medium high index of refraction.

Lens element 17 is similar to element 11 but is much thicker. It iscemented to element 16 and is a concave; convex lens made of flint glasswith a high index of refraction. Lens element 18 is a concave-convexlens made of flint glass having a medium low index of refraction. It isseparated from lens 17 by an axial length S I It is necessary to usepositive lens elements, such as lenses 12 and 16, in an objective lenssystem of this type in order to obtain sufficient positive power and ashort focal length. It is also necessary to use all the negativeelements to correct for astigmatism, flatness of field, and chromaticaberration. Distances S and S, are larger in order to increase thediameter of the incident light beam when it enters the positive lenselements.

Lens systems in the past have used internal prisms, but the presentinvention is novel in the use of an internal prism in a wide angleobjective lens system, and in an objective lens system which has its twooutermost elements negative in power.

The first correction for coma is made by the use of a nearly symmetricalarrangement of lens elements on the two sides of the central prism 14.The residual coma is substantially reduced to zero by the choice ofglass and radius values along with lens thickness.

The spherical abberration is brought substantially to zero by the shapesand powers of all the elements, but primarily by the surfaces betweenelements 12 and 13, and between elements 15 and 16.

The following table gives the optical characteristics of the lens systemshown in the drawing and described above. The numbers are in units,where the focal length 100, and back focal length 24.1.

Lens Radius Thickness(t) Refractive Disper- No. (F=) Air Space(s) Glasslndex=N sion 10 R, 190.38 I, 17.54 C 1522x005 59.51

R, 41.627 I 11 R, 80.935 .r 36.48 C 1.7881005 505:2.5

R 44.987 1; 7.01 12 R,=- 37.194 t,=45.88 C 1.5921005 58.5:25 13 Rl03.752 r.=4.91 C 1.5232005 515:2.5 I4 R-,= s;=.07 F 1.8-:1 50:15.

R. w I. 44.55 15 R, 660.813 s; .07 C 1.5232005 51512.5

R 35.054 1. 4.21 16 R 42.946 1, 35.85 C 1658x005 50.5fl.5 17 R p-157.627r 18.24 F 1.7841005 26.5fl.5 18 Ry 37.088 30.87 F 1.5411005 47.5125

where C Crown Glass and F Flint Glass.

It will be noted that the two outer negative lens elements are separatedfrom the adjacent elements by a considerable space, amounting todistances between 0.25 and 0.4 times the focal length of the system.This separation is required in order to make the optical light beamsubstantially larger at the positive lens elements than at the negativelens elements. The combination of the first negative element 10 plus thenext positive cemented combination ll, 12, and 13 brings the incidentlight rays to an approximately parallel condition. This substantialparallelism of the rays provides the best location for the prism 14.

Having thus fully described the invention, what is claimed as new anddesired to be secured by Letters Patent of the United States, is:

1. A wide angle projection lens constructed in accordance with thepresent invention comprising the lens elements as set forth in thefollowing table:

where C Crown Glass and F I Flint Glus.

RP- 37.194 R 103.752 R110: fh-m R 660.8[3 R 35.054 R 42.946 R P-157.627R 37.088 R14- l03.40l

l.523:t.005 5|.5i'2.5

1. A wide angle projection lens constructed in accordance with thepresent invention comprising the lens elements as set forth in thefollowing table: Disper- Lens Radius Thickness (t) Refractive sion No. F100 air space(s) Glass index(ND) (V) 10 R1 190.38 t1 17.45 C 1.522 +OR - .005 59.5 + OR - 2.5 R2 41.627 11 R3 80.935 s1 36.48 C 1.788 + OR -.005 50.5 + OR - 2.5 R4 44.987 t2 7.01 12 R5 - 37.194 t3 45.88 C 1.592 +OR - .005 58.5 + OR 2.5 13 R6 - 103.752 t4 4.91 C 1.523 + OR - .00551.5 + OR 2.5 14 R7 infinity s2 .07 F 1.8 + OR - .1 50 + OR -
 15. R8infinity t5 44.55 15 R9 660.813 s3 .07 C 1.523 + OR - .005 51.5 + OR -2.5 R10 35.054 t6 4.21 16 R11 - 42.946 t7 35.85 C 1.658 + OR - .00550.5 + OR - 2.5 17 R12 -157.627 t8 18.24 F 1.784 + OR - .005 26.5 + OR -2.5 18 R13 - 37.088 s4 30.87 F 1.541 + OR - .005 47.5 + OR - 2.5 R14103.401 t9 14.03 where C Crown Glass and F Flint Glass.